Structural abnormalities are found in the brains of schizophrenics. They affect preferentially, but not exclusively, medial temporal lobe structures (parahippocampal gyrus, hippocampus and amygdala), and can be found in all sub-types of schizophrenia. The structures of the medial temporal lobe are believed to have a crucial role in the integration and processing of the output from association cortex. It is probable that all schizophrenics have abnormalities in the medial temporal lobe that differ in degree but not in kind. Dysfunction of this system could result in the clinical symptoms that form the core of the schizophrenia syndrome. The changes in brain structure are not the result of neurodegenerative processes or destructive lesions but suggest a disturbance in the normal pattern of brain development.